Lead Placement

     Electrocardiographic electrodes, or leads, are used to record electrical potential at the surfaces of the body.  Different arrangements of the leads produce corresponding patterns with the ECG.  For more information about other leads used, consult Dukes' Physiology of Domestic Animals and Ettinger's Small Animal Internal Medicine.  Although there are up to 12 leads that are used in electrocardiology for vector analysis, we will focus on the two most frequently used to monitor veterinary patients under anesthesia:

    Three electrodes are used:  right arm (usually white), left arm (usually black), and left leg (usually red).

Lead II - RA is negative with respect to LL; LA is indifferent.

• Used most frequently in veterinary practice for canine, feline, and avian species as well as most smaller exotic species

• Place electrodes as follows:   Right arm at the elbow, left leg at the stifle region, and a ground lead (the left arm at the elbow)

• Click here for an image of lead II placement on a dog

Base-Apex - (dial lead I) RA is negative with respect to LA; LL is indifferent.

• Used in large animal species such as equine, bovine, and caprine patients

• Place electrodes as follows:  Right arm is attached to the skin at the dorsum of the base of the neck just cranial to the scapula and withers, left arm is attached on the chest just caudal to the point of the elbow (about the 5th intercostal space), and the left leg is attached at the stifle region

• Click here for an image of base-apex lead placement on a horse

Other Species:

• Click here for an image of lead placement in a snake

• Click here for an image of lead placement in the avian

• Click here for an image of lead placement in the iguana